1. Field of the Invention
This invention relates to an optical apparatus such as a lens barrel or a camera having a zoom mechanism.
2. Related Background Art
Heretofore, the driving of a power zoom lens driven by a motor has been effected by a motor and a cam ring. That is, design has been made such that each group constituting the zoom lens is moved by the use of a cam ring, and the zoom lens has been driven by rotating this cam ring by a motor.
However, an attempt to drive all groups by the interlocking of a cam gives rise to a limitation in the downsizing of a zoom lens barrel. Also, the required dimensional accuracy of the cam becomes more and more severe for a lengthened focus of zoom.
The use of a plurality of drive sources, to move the groups independently of one another would seem to thereby make the lens barrel compact. Also, if the respective groups can be moved independently of one another, even complicated control will become possible by using calculating means such as a microcomputer, and it will also become easy to control a lens of the rear focus type which has been difficult to realize by the conventional driving system using only a cam.
However, where the zooming operation is performed by the use of a plurality of motors, there arises the problem that zoom control cannot be simply accomplished.
That is, the movement speeds of the respective groups entirely differ from one another depending on the driving system. For example, where a cam is used, even if the speeds of the motors are constant, the movement speeds are varied by the angle of a cam slot, and where helicoid is used, the movement speeds are proportional to the driving speeds of the motors. Generally, the positional relation between optical groups by zooming is not a linear relation and therefore, if the drive motors for the respective groups are simply driven at a constant speed, the relation will become such that the movement of some group is great and the movement of other groups is small.
An attempt to control the speeds of the motors to thereby satisfy the relation between the optical groups would result in very complicated control, and this will be impossible if considered as an extension of the conventional motor driving method.